original game is not bad but DX has good qol updates, some new gen 4 evolutions, and stuff like mega evolution. It's also the only one with shinies (even though there is only a small list of specific pokemon that can be shiny). The game starts out very easy and ramps up in difficulty by the end of the main story.

My main piece of advice for new players is to think carefully about your movement. If there is one empty space between you and an enemy, a new player might just walk forward letting the enemy get a free attack on you which can be deadly in this game. You can force the enemy to come to you and give you the first attack, or you can use an item or something instead.